The use of weather resistive coatings in construction applications has been on recent increase in the building and construction industries. Such coatings protect buildings from water infiltration. They may also provide air barrier properties, whereby air ingress and egress is minimized, and this in turn reduces heating and cooling costs for the building owner. These coatings may be applied to roof decks as waterproofing and may be applied over insulation to prevent ignition in the event of fire.
Air barriers can be applied to the building exterior as self-adhering membranes or liquid coatings. It is desired that liquid-applied products be water-based rather than solvent-based for health and safety reasons. It is also desired that membranes to be applied using a single component spray, because two components require spray equipment that is more complex and costly.
Many requirements for air barrier performance exist. Due to possible building movement and settling, air barriers should have elongations exceeding two hundred percent (200%). Air barriers should also possess good adhesion when applied to conventional construction materials, such as exterior gypsum board, concrete, and the like. Since air barriers are used throughout North America, such products should possess low temperature flexibility, and should avoid cracking and brittleness when used in cold winter conditions. Air barrier products should also be soft enough to provide sealing around nails and fasteners, and should be designed to resist degradation from UV and heat if left exposed during construction.
Air Barriers can be classified as either vapor permeable or impermeable with respect to water vapor. For purposes of the present invention, the term “impermeable” and the concept of water vapor impermeability shall mean and refer to less than 1 perm (5.70×10−8 g/Pa·s·m2) when tested according to ASTM E96B-10, and the term “permeable” and the concept of water vapor permeability shall mean and refer to greater than 10 perms (5.70×10−2 g/Pa·s·m2). (Note: whether permeability or impermeability is specified for a particular application will often depend on building design and location).
The 2012 international building codes require buildings having a height exceeding 40 feet to have a weather resistant barrier. If the barrier material is combustible, the barrier must pass requirements under NFPA 285 which requires full scale assembly testing for flame spread which should not exceed eight feet from point of ignition. Alternatively, the building design and materials may be assessed using cone calorimetric procedures in accordance with ASTM E 1354-04 which involve calculating the exothermic amount of heat per unit time for materials exposed to an incident heat flux and ignition source. It is general knowledge that standard air barrier formulations are highly flammable and that flame retardants need to be incorporated into the air barrier to meet requirements under applicable codes and regulations.
However, flame retardants have attendant advantages and disadvantages. One class of flame retardants are halogenated materials, which give rise to environmental concerns. On the other hand, hydrated mineral fillers such as magnesium hydroxide and aluminum trihydroxide are popularly used for their ability to generate water molecules during combustion and to decrease overall temperature and thus fire spread. The disadvantage of these types of fire retardants, however, is that they require high loading levels which may deleteriously impact the mechanical properties of the air barrier (See “The Application of Hydrated Mineral Fillers as Fire Retardant and Smoke Suppressing Additives for Polymers,” by Peter R. Hornsby, Macromol. Symp. 108 (Huthig 84 Wepf. Verlag, Zug. 1996), pp. 203-219. In U.S. Pat. No. 7,504,451, Brown et al. describe a combination of aluminum trihydrate and clay for generating a char layer to improve fire retardant properties. However, clays are hygroscopic in nature and will increase water permeability of water vapor through the air barrier. Clays work most effectively when incorporated into polar polymers, which in turn have the disadvantage of having relative permeability to water vapor compared to other polymers that could otherwise be used. Another class of flame retardants is based on the use of phosphorus. These are most effective in polymers containing oxygen or nitrogen, but unfortunately phosphorous-containing polymers increase water vapor permeability.
Thus, a novel fire retardant air barrier having water vapor impermeability and desired mechanical properties such as low temperature flexibility and high elongation is needed.